This application is a U.S. National Stage of International application PCT/EP96/05659, filed Dec. 17, 1996, and published on Jul. 3, 1997 in the English Language.
The present invention concerns solid catalyst components comprising magnesium chloride and a titanium compound supported on metal oxides, and catalysts obtained from them.
Said components and catalysts find a particular application in the polymerization of CH2xe2x95x90CHR xcex1-olefins where R is hydrogen or an alkyl radical with 1-6 carbon atoms, or an aryl radical, in particular a phenyl radical.
In the art are known and described many examples of solid components and catalysts of the above mentioned type obtained by way of various preparation methods.
The interest in developing catalysts where the magnesium chloride and the titanium are supported on metal oxides is due to the many advantages that said catalysts offer, such as:
reduction in the content of halogens in the polymer obtained with said catalysts, due to their reduced content of halogens compared to the catalysts comprising a component supported on magnesium chloride;
simplicity in the preparation;
the availability in the market of metal oxides adequate for the preparation of the catalysts.
Obviously said reduction in the content of halogens is greater as the yield of the polymerization of the catalyst increases.
However, the catalysts comprising a component supported on magnesium chloride, and therefore not containing metal oxides, allow one to obtain polymers having higher bulk density compared to the catalysts having the magnesium chloride and the titanium compound supported on metal oxides.
For example, published European patent application n. 506074 describes catalysts supported on metal oxides that allow one to obtain high yields in the polymerization of olefins, however the examples show that the polymer obtained has a tamped bulk density which does not exceed 0.46 g/cm3.
Therefore, it would be particularly desirable to obtain a catalyst supported on metal oxides that would be capable of producing, with high yields, polymers having a higher bulk density.
In fact, a higher bulk density facilitates the conveying and processing of the polymers, and allows the polymerization plants to maintain high levels of productivity, particularly in liquid polymer.
As an answer to this need, the Petitioner realized a solid catalyst component for the polymerization of olefins, which constitutes one object of the present invention, comprising the product of the direct reaction, with no subsequent reactions with reducing organometallic compounds, between a titanium compound containing at least one Ti-halogen bond, optionally an electron-donor compound, and a support obtained by contacting a metal oxide containing hydroxyl groups with a solution comprising:
A) magnesium chloride;
B) an alcohol in quantities ranging from 1 to 6 moles, preferably from 2 to 4 moles, per mole of magnesium chloride,
in an organic solvent capable of bringing the magnesium chloride in solution in quantities greater than or equal to 5 g per liter, preferably greater than or equal to 10 g per liter in the presence of the above mentioned quantities of alcohol B), said solvent, however, not being able to form adducts with the magnesium chloride.
The catalysts obtained from the above mentioned solid component are capable of producing polyolefins in free-flowing particles having a tamped bulk density even higher than 0.5 g/cm3.
Moreover, said polyolefins contain a particularly small fraction of fine particles (i.e., having a diameter smaller than or equal to 500 xcexcm), generally less that 1% by weight, while the micro-fines (i.e., polymer particles with a diameter smaller than 106 xcexcm) are substantially absent. Said characteristic constitutes a further advantage, because low contents of fine particles contribute to facilitate the conveying and processing of the polymers. In addition, the absence of micro-fines contributes to the elimination of fouling and plugging phenomena in the polymerization plants and in the polymer conveyance plants.
A further advantage of the catalyst components of the present invention is the extreme simplicity of the process used for their preparation.
In fact there is no need for any physical or chemical treatment of the metal oxide before it is contacted with the solution of magnesium chloride and alcohol B) in solvent C). Moreover the reaction with the titanium compound containing at least one Ti-halogen bond is carried out by adding said titanium compound to the suspension of metal oxide in the solvent C), resulting from the contact with the above mentioned solution, or after removing the solvent C) from the suspension, preferably by evaporation. The reaction with the electron-donor compound, when used, may occur before, during or after the reaction with the titanium compound. The reactions with the titanium compound and the electron-donor compound, therefore, occur directly, without treatments or intermediate reactions after the contact between the metal oxide and the solution of A)and B) in C), other than the removal of C) and partial removal of B) (both being optional), and without further reactions with reducing organometallic compounds.
Said preparation process is particularly simplified compared to the process described in published European patent application n. 408 750, which requires the use of solutions of magnesium chloride and alcohols in organic solvents, but needs to carry out the following steps:
treatment of the metal oxide, before the contact with the above mentioned solutions, with an organometallic compound of the groups from II to IIIA of the periodic table, or with a halogenated compound;
treatment of the product of the contact with the above mentioned solutions, either before, during or after the reaction with a titanium compound, with a reducing organometallic compound.
In addition, in all of the examples of the above mentioned European patent application, the metal oxide is previously subjected to heat treatments. The same examples show that in spite of the complexity of the catalyst preparation process, the polymer obtained from it has relatively low bulk density values. Moreover, the above mentioned catalyst is suitable only for the polymerization and copolymerization of ethylene, while the catalyst of the present invention is capable of producing highly isotactic polypropylene with all the advantages described above.
Particularly preferred among the metal oxides that can be used in the preparation of the solid catalyst component of the present invention are the silica, alumina, the mixed Al and Si oxides, magnesium oxide, and titanium dioxide.
As already stated, the metal oxides are not subjected to physical or chemical treatments before being contacted with the magnesium chloride solution, therefore they contain hydroxyl groups in quantities generally ranging from 1 to 3 mmoles per gram.
Preferably they contain also free water, i.e., water that is not chemically bonded but is only absorbed into the metal oxide, in quantities generally up to 15 mmoles per gram, in particular ranging from 0.1 to 15 mmoles per gram. The determination of the quantity of hydroxyls can be made according to the method described in J. Phys. Chem. 66 800 (1962), and that of the free water by way of the Fisher reagent.
Preferably the metal oxides have a pore volume (B.E.T.) greater than 0.3 cm3/g, and generally ranging from 0.5 to 3.5 cm3/g, while the surface area (B.E.T.) of said oxides can vary within rather wide limits, for example from 30 to 1000 m2/g, preferably from 200 to 500 m2/g.
Examples of solvents C) are aromatic hydrocarbons, and aliphatic, cycloaliphatic, or aromatic halogenated hydrocarbons. The preferred ones are the halogenated hydrocarbons, in particular the aliphatic or cycloaliphatic chlorinated or brominated hydrocarbons, either saturated or unsaturated, or aromatic hydrocarbons, containing 5-20, more preferably 6-12 carbon atoms.
Specific examples of aromatic hydrocarbons are: benzene; toluene; xylene; ethylbenzene; isopropylbenzene. Specific examples of halogenated hydrocarbons are: CH2Cl2; CHCl3; CCl4; CHCl2Br; i.-C3H7Cl; n.-C4H9Cl; CH2Clxe2x80x94CH2Cl; CHClxe2x95x90CCl2; CH2ClCHCl2; C6H11Cl; C6H10Cl2; C6H5Cl; C6H5Br; C6H4Cl2; C6H5CH2Cl; ClC6H4CH2Cl; C6H5CCl3; CH2Clxe2x80x94CHClxe2x80x94CH2Cl; CH2xe2x95x90CHCH2Cl; CH3C6H4Cl.
Preferred examples of alcohols B) are the C1-C25 aliphatic, saturated or unsaturated, C3-C25 cycloaliphatic, saturated or unsaturated, and C6-C25 aromatic mono- and dialcohols (i.e., containing one or two hydroxyl groups), said mono or dialcohols optionally containing one or more halogen atoms, in particular chlorine and bromine.
Specific examples of alcohols B) are: CH3OH; C2H5OH; i.-C3H7OH; n.-C4H9OH; i.-C4H9OH; CH2OHxe2x80x94CH2OH; HOxe2x80x94(CH2)3xe2x80x94OH; OHxe2x80x94(CH2)12xe2x80x94OH; ClCH2CH2OH; CL3CCH2OH; C6H5OH; CH3-C6H4OH; C6H5xe2x80x94CH2OH; C6H11OH; C6H10(OH)2; C16H33OH; C10H20(OH)2; CH2xe2x95x90CHxe2x80x94CH2OH; CH2xe2x95x90CHxe2x80x94CH2xe2x80x94CH2OH; ClC6H10OH; ClC6H4OH; C12H23xe2x80x94C6H4OH.
The magnesium chloride and alcohol B) solution in solvent C) is obtained by mixing together the above mentioned components, which can be added in any order, and optionally heating until the magnesium chloride is completely dissolved.
At the same time or after the preparation of the above mentioned solution, one adds the metal oxide, which is preferably maintained in contact with the solution at ambient temperature or higher, for a period of time ranging from 10 to 120 minutes.
Preferably the concentration of magnesium in the solution is comprised from 0.05 to 1 moles/liter, more preferably from 0.2 to 0.5 moles/liter, while the metal oxide is added to the solution in quantities preferably ranging from 10 to 200 g/l, more preferably from 50 to 150 g/l.
The product of the contact of the metal oxide with the magnesium chloride and alcohol B) solution in solvent C) is then caused to react with the titanium compound, preferably after solvent C) has been removed by evaporation.
The evaporation of solvent C) can be carried out in a rotating evaporator for example.
Generally one operates under temperature and pressure conditions that cause a substantially total evaporation of solvent C), and optionally a partial removal of alcohol B). Preferably the operation takes place at reduced pressure. The titanium compound is normally used in excess with respect to the moles of alcohol B) present in the solution or in the solid product resulting from the removal of solvent C). Preferably the titanium compound is titanium tetrachloride. In this case the reaction is preferably carried out using said tetrachloride as the reaction medium after solvent C) is removed. The operation takes place at temperatures ranging from 0xc2x0 C. and 135xc2x0 C. for a period of time ranging from 0.25 to 1 hour or more. After the reaction, the excess TiCl4 is removed hot, and the solid is repeatedly washed with a hydrocarbon (such as hexane, for example) until all the chlorine ions have disappeared. It is advantageous to repeat the treatment with TiCl4 one or more times, and wash the solid as indicated above.
As previously stated, the reaction with the electron-donor can be carried out at the same time as the one with the titanium compound. In the case of TiCl4, the electron-donor compound is dissolved or suspended in the excess TiCl4, and the solution or suspension is caused to react with the metal oxide. The quantity of electron-donor compound used preferably ranges from 0.1 to 1.5 moles per g-atom of Mg, more preferably from 0.2 to 0.4 moles.
The electron donor compound can also be caused to react before or after the reaction with the titanium compound besides during the reaction with the titanium compound. In the case where it is caused to react afterwards, it is best if the reaction takes place in an aromatic hydrocarbon medium such as benzene or toluene, and the quantity of electron-donor compound be equimolar with the titanium compound fixed on the metal oxide.
The best results, however, are obtained by reacting the electron-donor compound at the same time as the titanium compound.
Other titanium compounds that are suitable for use besides the titanium tetrachloride, are the halogen alcoholates, such as TiCl3OR, where R is a phenyl radical for example, and the trihalides, particularly the TiCl3.
For the catalyst components to be used in the stereoregular polymerization of xcex1-olefins, particularly for the production of highly isotactic polypropylene, it is preferable to use tetravalent titanium compounds.
Given the absence of treatments with the reducing organometallic compounds in the preparation process of the catalyst component of the present invention, the titanium present in said catalyst component can be maintained at a state which is substantially tetravent.
Any electron-donor compounds capable of forming complexes with the magnesium halides and/or the titanium compounds can be used for the preparation of the catalyst component. Examples of compounds that can be used are the ethers, esters, ketones, lactones, and compounds containing N, P, and/or S atoms. Preferred compounds are the dicarboxyl aromatic acid esters, such as phthalic acid, and malonic, pivalic, succinic, and carbonic acid esters.
Particularly suited are also the ethers described in published European patent application n. 361494 having the formula: 
where R, R1, and R2, equal or different, are linear or branched C1-C18 alkyl groups, C3-C18 cycloalkyl groups or C6-C18 aryl, alkaryl or aralkyl groups, and R1 or R2 can also be hydrogen. In particular, R is methyl and R1 and R2, equal or different, are ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, neopentyl, isopentyl, phenyl, benzyl, or cyclohexyl.
Specific esters are diisobutyl, dioctyl and diphenyl phthalate, benzyl-butyl phthalate, diisobutyl and diethyl malonate, ethyl pivalate, ethyl-phenyl carbonate, diphenyl carbonate.
Typical ethers are 2,2-diisobutyl-1,3-dimethoxypropane, 2-isopropyl-2-isopentyl-1,3-dimethoxypropane, 2,2-bis(cyclohexylmethyl)-1,3-dimethoxypropane, 2,2-bis(cyclohexyl)-1,3-dimethoxypropane.
In the supports (after the contact with the magnesium chloride solution) the Mg content preferably ranges from 0.5 to 20% by weight; in the catalyst components the Mg/Ti ratio preferably ranges from 0.5 to 8.
The electron-donor compound is preferably present in molar ratios to the magnesium ranging from 0.1 to 0.5, in particular from 0.2 to 0.35. The total quantity of magnesium halide, titanium halide or halogen alcoholate and electron-donor present in the catalyst component ranges preferably from about 5 to 60% by weight.
The catalyst components form, with Al-alkyl compounds, preferably with Al-trialkyl, catalysts which are suited for the polymerization of CH2xe2x95x90CHR xcex1-olefins where R is a hydrogen or an alkyl radical with 1-6 carbon atoms, or an aryl radical, and mixtures thereof optionally containing minor proportions of a diene.
Representative Al-alkyl compounds are Al-triethyl, Altriisobutyl, Al-tri-n-butyl, and linear or cyclic compounds containing two or more Al atoms bridge-bonded by way of O or N atoms, or SO4 and SO3 groups.
The Al-alkyl compound is generally used in an Al/Ti ratio ranging from 1 to 1000.
In order to improve the stereospecificity of the catalyst, in many cases it is preferable to use an electron-donor compound, together with the Al-alkyl compound, in quantities ranging preferably from 0.01 to 0.25 moles per mole of Al-alkyl compound.
The electron-donor compound is selected preferably from the ethers, esters, silicon compounds containing at least one Sixe2x80x94OR bond (where R is a hydrocarbon radical, in particular C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, arylalkyl or alkaryl), and 2,2,6,6-tetramethylpiperidine
When the solid catalyst component comprises an ester of dicarboxylic aromatic acid, such as phthalic acid, or an ester of malonic, maleic, pivalic, succinic, or carbonic acid, the electron-donor compound to be used together with the Al-alkyl compound is selected preferably from the silicon compounds containing at least one Sixe2x80x94OR bond. Examples of said compound are phenyltriethoxysilane, diphenyldimethoxysilane, dicyclopentyl-dimetoxysilane, methyl, tert-butyl-dimethoxysilane, methylcycloexyldimethoxysilane.
When in the catalyst component is present an ether selected from those described in published European patent application N. 361494, the stereospecificity of the catalyst is sufficiently high, therefore there is no need to use the electron-donor compound together with the Al-alkyl compound.
The polymerization of olefins is carried out according to known methods, operating in liquid phase, in liquid monomer or in a solution of the monomer in an inert hydrocarbon solvent, or in gas phase, or also by combining polymerization stages in liquid and gas phases.
The polymerization temperature generally ranges from 0xc2x0 to 150xc2x0 C., preferably from 60xc2x0 to 100xc2x0 C. The operation takes place at atmospheric pressure or higher.
The catalysts are used for homopolymerization as well as copolymerization of olefins. In the case of copolymers, they are used for the preparation, for example, of random crystalline copolymers of propylene with minor proportions of ethylene and optionally of butene and superior xcex1-olefins, or elastomeric copolymers of ethylene with propylene optionally containing minor proportions of a diene (butadiene, 1,4-hexadiene).
In addition, the catalysts can be used in the sequential polymerization of propylene, as well as mixtures of propylene with ethylene and/or butene and superior xcex1-olefins, to form impact grade polypropylene.
Prior to polymerization, the catalysts can be precontacted with small quantities of olefins (prepolymerization) operating either in suspension in a hydrocarbon solvent (such as hexane or heptane), and polymerizing at temperatures ranging from ambient to 60xc2x0 C. thus producing quantities of polymer ranging from 0.5 to 3 times the weight of the solid catalyst component, or operating in liquid monomer, thus producing quantities of polymer up to 1000 g per g of solid component.